1. Field of the Invention
This invention relates generally to oil well cementing compositions and particularly to lignin-based additives to cementing compositions for reducing fluid loss from the cementing composition to the surrounding subterranean formation which the well has penetrated.
2. Description of the Related Art
Cement compositions are used in the oil and gas industry to cement the annular space in the well bore between the casing and the surrounding formation. Cementing is done not only to secure the casing firmly in place but also to cement off permeable zones of permeable formations into which valuable materials may be lost and to prevent the intrusion of extraneous matter into the petroleum fluid producing zone.
Typically, a cement slurry is pumped downwardly through the tubing within the well casing and flows out of the open lower end of the casing at the well bottom. It is then forced upwardly around the casing in the annular space between the outer wall of the casing and the wall of the wellbore. Commonly, additives of various sorts are added to the cement slurry to control thickening times, weight, strength, and other characteristics of the cements to accommodate the wide variety of temperatures and pressures of various types of oil and gas wells.
When hydraulic cement is placed within or next to a porous medium such as the earthen strata of a well bore, there is often a tendency, especially in deep wells where high temperatures and pressures are common, for water to filter out of the cement slurry and into the surrounding strata. This fluid loss is undesirable because it may lead to contamination of the formation by the cement filtrate, premature setting of the cement, and reduced compressive strength of the set cement. To combat and control fluid loss in the well cementing process, various additives known as fluid loss agents have been discovered and employed in the industry. Examples of commonly used fluid loss control additives include cellulose derivatives such a carboxymethyl hydroxyethyl cellulose (CMHEC), and hydroxyethyl cellulose (HEC), and polyethylene amines, naphthalene sulfonates, polymer latex, polyacrylamides, and combinations of these. The particular fluid loss control additive used depends upon many factors such as the particular cement used, the temperature and pressure to be encountered in the well, and the depth of the well. The expense of the additive is a factor, especially in deep wells where a large quantity of cement must be used.
It would be desirable to have a fluid loss control additive derived from a readily available and relatively inexpensive material such as lignin, which is produced in large quantities as a byproduct of the pulp and paper industry. Lignin-derived compositions are already used in cement slurries as set retardation agents, as disclosed in U.S. Pat. Nos. 3,375,873; 3,662,830; 3,821,985; 4,047,567; 4,065,318; 4,296,813; RE 31,190; and RE 31,127. U.S. Pat. No. 4,125,160 and U.S. Pat. No. 4,131,578 teach a method and composition for a fluid loss additive composed of a blend of a polyamine, a lignoamine and/or lignosulfonate, a borate ion releasing compound and a carbonate and/or bicarbonate.